Historically, architects have held responsibility for completing the architectural interior of buildings, although artisans, craftsmen, furniture makers and — more recently — interior decorators have played a role. Beginning in the mid-1900s, the idea of the speculative building and a shift from corporate ownership to leasing began to separate the design of the building from the design of its interior. Urban cores have aged, prompting the need for interior renovation of still viable building shells. More importantly, an increasing complexity associated with the building interior — in workplace, healthcare, institutional and other types of environments — required an increased expertise and an increased level of specialization in professional services. This trend toward specialization continues,